Yarbro takes an unusual tack in her latest adventure (after Communion Blood) for the worldly vampire Saint-Germain. In lieu of locating her vampire hero at a specific historical hot spot, she presents a plot that sprawls across 500 years, and for the familiar human heavies she substitutes a vampire villainness of the benevolent bloodsucker's own creation. While traveling through Spain in the seventh century, Saint-Germain, against his better judgment, saves the life of the mortally wounded Csimenae through a mingling of their blood. Despite his efforts to instruct her in the necessity of unobtrusive coexistence with humans, the haughty, impetuous Csimenae intimidates her countrymen into worshiping her and her son, Aulutis, eventually driving her vampire mentor away. Over the next 500 years, Saint-Germain's travels bring him into contact several times with Csimenae, who engenders a personal vampire army that preys on both unwary pilgrims and invading Moors. Yarbro's impressive historical research allows her ample opportunity to parallel Csimenae's exploits to the Muslim plunder of the Spanish countryside and the siege spirit that infected medieval Europe. Though the incessant details of daily life in the Dark Ages can grow wearisome, they are offset by Saint-Germain's poignant moments of soul-searching over his rare, regrettable moment of fallibility. The chronicles of Saint-Germain total more than a dozen books, but the unexpectedly original angle of this novel offers an infusion of fresh blood that could make it one of the series' most popular entries; it also suggests that Yarbro has other surprises to spring in future volumes. (Oct.)